To determine a Marlin levergun's DOM (if the SN doesn't have a letter prefix), just:

* Subtract the first two digits from 2000 for guns made before Y2K, as in SN23578xxxx equals 2000 - 23 = 1977.

OR if that doesn't work,

* Subtract the first two digits from 2100 for guns made after Y2K, as in SN 97815xxxx equals 2100 - 97 = 2003.

Letter prefixed SN's started with an "C" prefix in 1946 to "Z" in 1964, then "AA" in 1965, "BB" in '66, "AC" in '67, and then "AD" & "68" in '68.
1969-72 used the year as a prefix before going to the subtraction system above.